In recent years, in a viewpoint of resource saving efficiency, direct-injection engines having superior fuel efficiency have been attracting attention. It is necessary for the direct-injection engine to inject high-pressure fuel from an injector. In the related art, a high-pressure pump is known in which a plunger reciprocates inside an inner wall surface of a cylinder so as to suction fuel supplied from a low-pressure pump installed in a fuel tank, to pressurize the fuel in a pressurizing chamber, and to pump the fuel to the injector side.
In the high-pressure pump, the fuel leaking out from the pressurizing chamber to a non-pressurizing chamber side through a clearance between the cylinder and the plunger has a high temperature due to heat generation. In general, an end of the plunger away from the pressurizing chamber is arranged near an engine and is likely to receive heat from the engine.
If a temperature of the high-pressure pump increases, there is a possibility that vapor lock or seizure of a plunger slide portion occurs inside the high-pressure pump. For example, a fuel supply device disclosed in Patent Literature (JP 3295678 B) as a countermeasure thereof suppresses an increase in the temperature of the high-pressure pump by introducing low-temperature fuel supplied through a cooling fuel passage diverging from a fuel supply passage into a cooling chamber inside the high-pressure pump.